This invention relates generally to an overcast system for use at an intersection of passageways in a mine. The overcast system includes adjustable stairways positioned adjacent to an overcast structure allowing people to cross over the overcast for passage along a mine passageway.
Overcasts are used in mines at passageway intersections to prevent mixture of ventilation air flow in the intersecting passageways and to maintain airflow along the desired path within a mine. An overcast is a tunnel structure that forms a flow conduit connecting two sections of a first passageway at an intersection of the first passageway with a crossing or intersecting second passageway. The overcast includes a pair of generally parallel spaced apart upstanding side walls and a deck or roof extending between and secured to the side walls. The side walls and deck form a flow conduit (tunnel) communicating between the sections of the first passageway. End and wing panels are used in combination with the overcast to form an overcast system that substantially closes off flow communication between the first and second passageways at their intersection. The normal airflow pattern is to have inlet air flowing through the overcast and return air flowing over the overcast. However, under certain circumstances, the airflow could be reversed. Overcast systems are known in the art as exemplified in U.S. Pat. No. 5,466,187 the disclosure of which is incorporated herein by reference. An airflow segregating structure like an overcast may also be erected by first excavating the mine floor. The deck is positioned over at least a portion of the excavated area and could be closer to the original floor than a typical overcast. This type of structure is referred to as an undercast. An undercast can use any suitable deck support erected adjacent opposite sides of the excavation to support the deck. Such support can be erected in the excavation and/or erected to the side of the excavation on the original mine floor. Such support can be, e.g., a block wall or could also be length extensible steel panels like those used to form stoppings as are known in the art. As used herein, the overcasts and undercasts will be referred to as air crossings.
Air crossing systems are effective to segregate the airflows between the first and second passageways at the intersection. However, they limit the ability of miners to utilize the second passageway since a wall is created across the second passageway. Personnel have found ways to get around the air crossing systems including some ways that may not be safe or reliable. Many times personnel will maneuver through gaps in the walls of the air crossing or in the wing panels sealing the air crossing to the mine walls. Sometimes ramps are formed at the air crossing sidewalls with back fill. Ladders could likewise be used, but mine floors can be rough and uneven making use of a ladder difficult and possibly dangerous. None of the foregoing ways of circumventing an air crossing would be very effective in the event an injured miner needs to be evacuated from the mine or if an emergency evacuation is needed.
The use of permanent and semipermanent structures in mines presents difficulty because mines are not static in their size and shape. Common phenomenon in mine passageways is convergence and divergence of the mine walls, floor and roof. A mine passageway will change in size and shape, sometimes significantly, due to the weight of the overburden over the mine passageway. The walls, floor and/or the roof may converge inwardly into the passageway. Also, and less frequently, the walls, floor and/or roof may diverge making the passageway larger. Both convergence and divergence may occur in a passageway. As used herein, the phrase "dimensional instability" includes both convergence and divergence.
Dimensional instability can cause problems with any structure installed in a mine passageway. Structures may shift or try to change dimensions or become separated from a wall, floor, roof or one another. The position of a structure may also change. Dimensional instability presents potential structural integrity problems for any structure positioned in a mine particularly with the ability of a mine to apply tremendous forces to a structure. Thus, mine equipment has special design needs to be able to accommodate dimensional instability. For example, an opening or door in an air crossing may not be available or workable from time to time, because of structural movement or improper maintenance, as a means to cross from one side of an air crossing to the other side. Further, equipment such as conveyors may be positioned in the air crossing preventing a miner from traversing across the air crossing from side to side. High airflow rates and pressure differentials can also make doors difficult to use. In the event of an emergency, structures must work reliably to reduce risks by allowing personnel unimpeded and safe passage through a passageway. Likewise, in the performance of normal duties, structures should not be an impediment to miners.
Thus, there is a need for an air crossing system which controls airflow in a mine but which can be easily traversed by crossing over in one passageway and passing through in an intersecting passageway. The present invention utilizes a deck structure with an automatically adjustable stairway to form a walkway for conveniently and safely traversing from one location in a mine to another including the use of such structure as an air crossing or as a walkway to cross over mine equipment like large conveyor belts.